Insulating spacer



March 14, 1933. CROWLEY 1,901,703

INSULATING SPACER Filed April 9, 1931 lNil/LATIDN INSULI? T/ON INSULHTION NVENTOR flenr L- Crnw/ey BY CL A ORNEY5 Patented Mar. 14, 1 9 33 UNITED STATES HENRY L. CROWLEY, or ms'r ORANGE, NEW JERSEY, AssiGNoR TO- HENRY '1.'. Row

ORANGE, nnw'anasny, econronn'rron or new LEY & COMPANY, INC., or wns'r JERSEY PATENT OFFICE",

INSULATING SPACER Application filed'April 9, 1931. Serial No. 528,730.

This invention relates in general to insulating spacers "and more particularly tov such spacers as used in radio vacuum tubes for positioning the cathode with respect to the other electrodes. a

One of the objects of this invention is the provision of a spacer for supporting the cathode which is so constructed as to give a minimum of leakage between the cathodes andthe other electrodes, especially the-grid electrode.

A further object of this invention in volves the construction of a spacer and. its

relationship with the cathode to produce a.

minimum of strains, chemical reactions, including electrolysis at high frequencies and the temperatures involved and leakage. A further object of this invention is to construct spacers of'this nature of magnesia oxide which has a high dielectric resistance at high temperatures. 1

A further object of this invention is to produce 'a spacer which is nonporous, smooth or semi-polished or polished. 1 A still further object of this invention is to produce a spacer for magnesia oxide which is extremely thin but has suflicient mechanical strength for the purposes reuired. I

A still further object of this invention is to so construct the spacer supporting the cathode that there will be" a minimum of contact between the two and between the spacer and plate electrode in some of the forms disclosed.

These and many other objects as will appear from the following disclosure are secured by means of this invention.

This invention resides substantially in the combination,construction, arrangement and relative location of parts, all as will be described in detail below.

Referring to the drawing:

Figs. 1 and 2 are top plan views of two forms of spacers;

Figs. 3 and 4 are a top plan view and a side elevational view, respectively, of another form of spacer;

Fig. 5 is still a further modified form;

Figs. 6 and 7 are a top plan View and a side elevational view, respectivelyf'with. someparts broken away of a stillfurther modification.

In the manufacture of vacuum devices. 7 such as audion tubes used in the radioindustry, it is the present practiceto support the cathode with respect to the other'electrodes by-means of insulating spacers made of'micaylava and the like. @These spacers are at presentso constructed as to effect a maximum area of contact between them and thecathode. By reason ofthe material used in theficonstruction employed poor insulation results.

ther reduced'by the. deposition on theirsurp In thelaminated mica structure conduction through the entrained gases occurs. Theirinsulating propertiesarefup faces of particles'of the cathode coating def posits from the magnesia flash, nickel smudge and the like. In addition, theseinsulators do not have a sufiiciently'highdielectric distance at the high operating peratures of such devices. I

The general object of this invention is to overcome these difficulties. The'm'agnesia tem- J spacer of this invention is composed in part, 2

or is completely madeof magnesia oxide in accordance with the disclosure in my co--.

pending application Serial No.832,555, filed January 14, 1929, and my c'opending application Serial No. 528,732 filed April 9, 193-1.

Briefly, such a spacer is made from magnesia oxide and a binder or flux; a mixture of which is fired at the proper temperature to burnout the flux. Where the resulting body is too brittle due to vitrification, I

find it desirable as disclosed may copend lng cases above mentioned to use precipitat ed magnesia and talc as the binder or flux.

Aniixture of these whenpre-tre'ated results in a suflicientiy strong and yet materially softer bodywhich iseasy to grind andm'a chine to" desired form. Instead of using precipitated magnesia the metalfm a'y be burned to an oxide. Either form of magnesia may bepre-fired before mixing with the talc for the final firing which'gives' a product which is less-liable to shrinkage.

It is well to use as pure materials as possible,since impurities tend to cause vitrifica 2 area of contact with the spaCQ T Th grid tion both in the pre-firing andfinal firing.

The use of talc is important because it results in a relatively soft body.

As far as 'thisinvention is specifically concerned, it is immaterial of what substance the spacer is formed or how it is prepared,

' since the invention in this case is confined to the form of the spacer.

Referr ng to the drawing, the ceramic cathode supporting body is shown at l-in j the form of a cylindrical rod having two fine longitudinal bores 2. This rod may be made of any desired materials andin accordance with any process, such as that dis. closed in my above mentioned applications;

Within the fine bores is mounted the cathode or heater (not shown) in the form of a fine wire shaped like a hairpin. At3 is shown aspacer which is substantially rectangular with its four corners removed. -:At the center of the spacer is a square hole/4 which is so'shaped so as to nicely, fit around the support 1 and contact thercwithat fourpoints. Surrounding; the spacer 3 isv the plate electrode 5 which likewise has a very limited (not shown) is supported withinlthe plate and surrounding the cathode and 'may be partially supported on the spaceror entirely supported from the stem of the tube in any well-known manner.

7 twill be seen by this construction that there is a minimum of area contact between-the cathode. structure l and the plate 5 without in any way detracting from the supporting and spacing functions of the spacer. Another important advantage of this construction is that the openings between the different elements permits ofa fr-eecirculationof the gases; In

other words, ventilating effect is produced which keeps the temperature of the assembly in use at alower point than it would be if these openings were not provided; 1

In the modifiedarrangement in Fig. 2 the spacer 6 is elliptical in outline and is pro.-

Yvided with an elliptical opening 7 which holds the support 1 and the plate or grid. 5

in proper relation. 7

In the structure of Figs. 3 and 1 theceramic supporting rod 8 is square and lies within acircular opening 10 in thecircular spacerdisc 9. V j A Q The modification in Fig. 5 shows a spacer for use with a so-called screen grid tube in 'whichthe outer screen'grid 10 is in the form of a cylinder closed atone end. The closed end is providedwith a relatively large cir-' cu lar opening 11 which is of greater diameter than'the diameter .of the supporting body. 1. Secured to the grid 10, by means of rivets 14- or other. suitable fastening means, is the insulating spacer 12 provided 'with a square'central opening 13 through which the insulating body 1 projects slightly. V

port 1.

The modification in Figs. 6 and? involves a spacer 15 having radial. projections 16; This spacer is provided withan elliptical central opening 17 through which the rod 1 projects. At, 5 is the plate contacting with the radial lugs 16. The spacers are also provided with anotherho'le' through which I v the grid supporting wire 18 projects. This wire or rod is provided with a collar 19 againsit which the spacer rests. The grid can be supported from the rod '18 within the plate 5 and surrounding the cathode sup- In all theforms of thisdevice which have been Shown forth'e purpose of illustrating this invention, the area of contact between by is at'a minimumand openings areleft to give a ventilating'effect; I

It will be seen from the abovedisclosure thatthis invention relates to certain principles of construction which maybe embodied in other physical forms than those givenfor purposes of illustration, I do not, therefore, desire to be strictly limited to, the disclosure so I the spacer andthe elements supported thereasgiven, but rather to the scope of the ap pended claims.

What I seek to secure States I Letters Patent is:

1. The combination as described comprising a ceramic support, a ceramic spacer having peripheral lugs, the spacer. having an opening through which the support projects of different shape. than the cross-sectional shape of the support, and an electrode in contact with said lugs. 2. In anelectron dischargedevice-the com-' bination including an electrode and a cathmy hand on this 6th day of April 1)., y

- HENRY L. CROWLEY. 

